Process for electrochemical conversion

ABSTRACT

In an electrochemical process, the reaction takes place within the confines of a porous electrode element. The feed materials are introduced into the bottom of this porous electrode element by means of a sparger which is positioned within the bulk of the electrolyte adjacent a bottom surface of said electrode element.

I limited States Patent [151 3,660,255 Fox et a1. 1 51 May 2, 1972 1PROCESS FOR ELECTROCHEMICAL ences Cited CONVERSION UNITED STATES PATENTS[72] Inventors: Homer M. Fox; Forrest N. Ruehlen; Keith 2,592,144 4/1952Howell et a1. ..204/247 X 1 A. Williams, all of Bartlesville, Okla.3,280,014 10/1966 Kordesch et a1. ...204/74 X Assign: Phillips Petroleump y 3,461,050 8/1969 ChildS ..204/59 [22] Filed: Sept. 24, 1970 PrimaryExaminer-John l-l. Mack Assistant Examiner-Neil A. Kaplan 1 PP 75,291A!torneyYoung and Quigg Related US. Application Data 57 ST v in anelectrochemical process, the reaction takes place within [63 I Commudnonof June 1968 the confines ofa porous electrode element. The feedmaterials abandoned are introduced into the bottom of this porouselectrode ele- 52 us. C1 ..204 59, 204/72, 204/246, ment y means ofSparger which is Positioned within the bulk 204 of the electrolyteadjacent a bottom surface of said electrode 51 Int. Cl ..B0lk 3/00element- [5 8] Field of Search ..204/59 72-81 0 Cl 10 D 27 1 aims,rawlng Figures PATENTEDMM 21972 3, 660,255 sum 2 BF 2 INVENTORS F. N.RUEH LEN H. M. FOX

BY K.A. ILITIAMS A T TORNEVS CROSS REFERENCE TO RELATED APPLICATIONSThis application is a continuation of application Ser. No. 739,476,filed June 24, 1968, and now abandoned.

BACKGROUND OF THE INVENTION This invention relates to electrode elementsand processes for electrochemical conversion.

Porous electrode elements, particularly porous carbon anodes are widelyused in electrochemical conversion reactions. Generally, the utilizationof such elements has involved immersing the element in an electrolyteand passing an electric current through this electrolyte from thiselement to an oppositely charged element. At least a portion of thematerials within the electrolyte is converted into products at one orboth electrodes. In a variation on this process, an additional feedstockfor the conversion process is bubbled into the electrolyte through aporous electrode element, such as a porous carbon anode, to producestill different products.

Very recently it has been discovered that the reaction in anelectrochemical conversion operation can be carried out within theconfines of the porous electrode element itself. This type of operationis of particular utility in electrochemical fluorination because itmakes possible a simple one-step route to partially fluorinated productswhich had previously been difficult to obtain. Carrying out thefluorination reaction within the porous anode, in addition to makingpossible the direct production of partially fluorinated products, alsoallows operation at high rates of conversion and without the formationof substantial amounts of cleavage products generally produced by theolder methods when operating at high conversion rates. The feed to befluorinated is introduced into the porous anode at a point near itsbottom and the fluorinated mixture exits at the top of the anode,generally above the electrolyte level. Passage of the feed into the bulkof the electrolyte is avoided.

It is apparent that if the reaction is to take place within theelectrode element, larger electrodes are desirable in order to increasethe available surface area wherein the reaction takes place. Howeverwith larger electrodes, it has been found that an uneven distribution offeed material can result within the electrode.

Nonuniform distribution of the feed material results in a partial lossof the advantage of this type of operation with respect to theproduction of only partially fluorinated products; this is because insystems, for instance, utilizing a KF-2HF electrolyte, the fiuorinatingspecies are generated continuously throughout the submerged surface ofthe electrode element and thus, in areas where feed is not distributedproperly, the excess of fluorinating species will fluorinate theavailable feed all the way to perfluoro products, or even produceundesirable cleavage products. Also nonuniform feed distribution canresult in sudden contact of accumulated fluorine with accumulated feedmaterial or with hydrogen from the other electrode element to give anexplosive reaction. It can thus be seen that uniform distribution of thefeed material and, consequently, uniform contact of the feed materialwith the electrolyte at the point of reaction are of prime importance.

This problem of nonuniform distribution of the feed material can besolved to some extent by using feed distribution laterals in the lowerportion of the electrode element. However, these feed distributionlaterals, unless they are protected in some fashion, can becomeflooded'with electrolyte and become plugged on continued usage.

SUMMARY OF THE INVENTION It is an object of this invention to provide animproved process and apparatus wherein the reaction in anelectrochemical conversion process using a porous electrode element iscarried out within the confines of the electrode element.

It is yet a further object of this invention to provide for uniformdistribution of feed to a porous electrode element.

In accordance with this invention the feed materials in anelectrochemical process are introduced into a porous electrode elementby means of a sparger located within the bulk of the electrolyteadjacent to a bottom surface of the porous electrode.

BRIEF DESCRIPTION OF THE DRAWINGS In the drawings, forming a parthereof, in which like reference characters denote like parts in thevarious views,

FIG. 1 is a schematic representation of an electrochemical cellutilizing a sparger feed section in accordance with the instantinvention.

FIG. 2 is an enlarged view, partially in section of the rectangularelectrode of FIG. 1.

FIG. 3 is a cross-sectional view of the lower portion of a rectangularelectrode element and sparger in accordance with an alternate embodimentof this invention.

FIG. 4 is a cross section through another embodiment of the instantinvention wherein the sparger is surrounded by an electrolyte-containingannular area.

FIG. 5 is aview partially in section of the lower portion of anelectrode element in accordance with another embodiment of thisinvention wherein the sparger is positioned within a cavity drilled outin the bottom of a cylindrical electrode element.

FIG. 6 is a cross-sectional view of the lower portion of a rectangularelectrode element in accordance with another embodiment of the instantinvention wherein the electrode ele ment is a composite of differentgrades of porous material.

FIG. 7 is a cross-sectional view of the lower portion of a rectangularelectrode element in accordance with another embodiment of the instantinvention wherein the sparger is positioned below the bottom of a flatbottomed electrode element.

FIG. 8 is a cross-sectional view of the lower portion of a cylindricalelectrode element in accordance with another embodiment of the instantinvention wherein the sparger is an integral part of the electrodeelement.

FIGS. 9 and 10 are cross-sectional views of the lower portion ofrectangular and cylindrical electrode elements, respectively, inaccordance with the instant invention wherein the spargers are affixedto the electrode element by means of a screw connection.

DESCRIPTION OF THE PREFERRED EMBODIMENTS The spargers of the instantinvention can be positioned either within a cavity in the bottom of theelectrode element which cavity is open to the bulk of the electrolyte,as shown by FIGS. 1 to 6 and 8 to 10, or the sparger can be positionedbelow the bottom of a flat bottomed porous electrode element as shown byFIG. 7.

It is most remarkable that the electrodes of the invention can be fed insuch a simple fashion and that uniform distribution of feed can beassured by introducing the feed through a sparger which is positionedwithin the bulk of the electrolyte adjacent the bottom of the porouselectrode element. Even more remarkable is the fact that this can bedone and still maintain the required mode of operation wherein thereaction takes place within the confines of the pores of the porouselectrode element as opposed to taking place within the bulk of theelectrolyte.

In the embodiment utilizing a cavity, the size and shape of the cavitycan vary depending on the size and shape of the electrode element. Theshape of the sparger is preferably complementary to the shape of thecavity as shown in the drawings, although this is not essential. With acylindrical electrode, a hole can simply be drilled in the bottom of theelectrode to form the cavity. With a slab-type electrode the cavity cantake the form of an elongated recessed portion in the bottom of theelectrode. The cavity can also take the form of a large feeddistribution lateral drilled through all or most of the length of aslab-type electrode parallel to the bottom of the electrode and in opencommunication with the electrolyte at one or more points along thelateral, generally at each open end of the lateral; the sparger is thencentrally disposed within this lateral, the electrolyte filling theannular area around the sparger and said electrolyte being in opencommunication with the bulk of the electrolyte in the cell. This type ofarrangement is shown in cross section in FIG. 4; the section in FIG. 4is taken along an area through the drain hole.

A nonwetting electrolyte is used; therefore, the feed materials aregenerally far more compatible with the surface of the electrode elementthan is the electrolyte and apparently for this reason they are veryrapidly absorbed into the porous electrode element. Even in arrangementssuch as that shown in FIG. 7 the feed is immediately absorbed by theporous electrode element and does not bubble out into the electrolyteexcept for the distance it travels in going directly from the sparger tothe bottom of the porous electrode element, thus a1- lowing theessential mode of operation whereby the reaction takes place within theconfines of the pores of the porous electrode element.

A nonwetting electrolyte is one wherein the contact angle between theelectrolyte and the porous electrode material is greater than 90 inorder that the anticapillary forces will prevent substantialimpregnation of the small pores of the porous electrode element by theelectrolyte. Nonwetting electrolyte-electrode combinations can beobtained simply by a suitable choice of these cell components. Forexample, the metal fluoride-containing I-IF electrolytes commonly usedin fluorine generation or electrochemical fluorination are nonwetting tocarbon electrodes. If an electrode is wetted by an electrolyte, it canbe conventionally treated with a wet-proofing agent.

The sparger may either be connected to the porous electrode element orinsulated therefrom. Thus it may either be of the same potential as theporous electrode element or float in potential in between that of theporous electrode element and that of the other electrode element in thecell. For instance where the porous electrode element is an anode usedin electrochemical fluorination, the sparger must not be cathodic enoughto liberate free hydrogen as this will reduce the electrical efficiencyof the cell; it may either be in electrical connection with the anode ormay float in potential between the anode and cathode.

The sparger can be an integral part of the electrode element as shown inFIG. 8; it can be attached by means of insulating straps as shown inFIG. 1; it can be mechanically affixed for easy removal, for instance bymeans of a snap-on or screw-on connection as shown in FIG. 9; or it cansimply float unconnected from the porous electrode element as shown, forinstance, in FIG. 5. In embodiments where it is affixed by a quickremoval type of connection such as the screw connections of FIGS. 9 and10, it can either be affixed to a portion of the porous electrode or tothe metallic current collector and feed introduction channel. Theconnection can be direct or through a nonconducting adaptor.

The choice of the material to make the porous sparger is extremelyimportant. The sparger must give good distribution at very low flowrates, the low flow rates being required to give sufficient conversionof the feed per pass. Materials which are not wetted by the electrolyteare presently preferred. In electrochemical fluorination systems usingl-IF-containing electrolyte, porous carbon or porouspolytetrafluoroethylene (Teflon) are by far the preferred materials.Other materials which resist wetting by the electrolyte such as metalsor plastics can also be used if they are not corroded by the system andif the pore size can be small enough and uniform enough that thepressure drop is sufficient to keep the electrolyte out of the sparger.Plastic materials are particularly desirable in instances where it isdesirable to have an electrically noncon ductive sparger. In general,any plastic material which has suitable porosity, which is nonwetting,and which will physically and chemically withstand the environment ofthe cell can be used. Thus, polytetrafluoroethylene, high densitypolyethylene, polypropylene, and the like, can frequently be used.

The maximum pore size in the sparger depends somewhat upon the depth ofoperation. At a 12-inch depth, the hydrostatic head can sometimes besufficient to cause the electrolyte to invade pores larger than about 70microns. At shallower depths the largest pores can be a little largerwhile at immersion depths greater than l2 inches, the largest pores mustof necessity be smaller to avoid flooding of the sparger by theelectrolyte. To be safe in avoiding a few large pores, the average poresize of the sparger should be small, for instance, less than about 20microns. Thus, suitable porous materials having an average pore size of001-30, preferably O.l-l0 microns, can be used. The sparger should havea permeability in the range offrom about 0.001 to about 4, preferably0.02 to about 0.5 darcys. The total porosity or void space in the poroussparger is of less importance; it will generally total less than about35 per cent. The relatively small and uniform pores of the spargerallows the feedstock to be introduced into the electrode element from aplurality of points and in the form of a multitude of very smallbubbles.

The porous electrode element can be any porous electrode materialsuitable for electrochemical conversion reactions taking place withinthe confines of the electrode material, specifically within the pores ofthe electrode material. It can, for example, consist of a single pieceof uniform porous carbon. It can have a variable porosity with smallerpores at the bottom and larger pores at the top so as to enable deeperimmersion into the electrolyte. It can have variable porosity fromoutside to inside, with smaller pores in the core section and largerpores on the outside in contact with the electrolyte. It can also be athree-section sandwich" electrode element having large pores in theouter section surrounding a central core, the large pores being incontact with the electrolyte, and the core being comprised of animpermeable current conductive material such as nonporous carbon ormetal.

With such sandwich" embodiments, it is generally desirable that theouter section of the composite be relatively thin for uniformity ofconversion. For example, outer sections of about 1 inch or less, even0.5 inch or less, can frequently be utilized with advantage because theyprovide an improved surface to volume relationship. Thin sections ofsome highly porous materials frequently lack mechanical strength and,thus, such composite laminates are often desirable.

The optimum surface to volume ratio of the reaction section, or largerpore diameter portion of the electrode if it is a sandwich electrode,will depend upon a number of factors among which are the desired degreeof conversion and the depth of the electrode immersion. For example, inthe electrochemical fluorination of a feedstock such as ethylenedichloride, a a surface to volume ratio of about 2 in. l is satisfactorywhen the sandwich" electrode immersion is about 12 inches and thehydrogen conversion is about 50 per cent. Ordinarily, surface to volumeratios from about I to about 3 in. 1 are used but, as mentioned above,this is dependent upon other conditions, and ratios of up to about 10in." can be used with some combination of conditions which include veryshallow electrode immersions. The surface to volume ratio is computed asthe electrogeometric surface, in square inches, of the reaction section,divided by the volume, in cubic inches, of the reaction section. Theelectrogeometn'c surface is the geometric working surface, of the highpore diameter reaction section, which is below the electrolyte level andactually in contact with the bulk of the electrolyte. The volume of thereaction section is simply the geometric volume which is below theelectrolyte level and exclusive of any core components.

In the porous electrode element, the average pore diameter of the porousreaction section will generally be in the range of l to 150 microns,preferably between 40 and 140 microns, and still more preferably between50 and 120 microns. These values depend somewhat on the depth ofimmersion of the electrode with deeper immersions requiring somewhatsmaller pores. Generally the permeability of such electrodes will be inthe range of 0.5 to 75 darcys, preferably from about 5 to about 75, andstill more preferably to 70, darcys. In general the total porosity willbe in the range of about to about 60 per cent.

The feed material is discharged into the cavity where it is rapidlyabsorbed into the porous electrode element. While it is not desired tolimit the invention to any theory of operation, it is believed that theelectrolyte partially penetrates the electrode through some of thelarger pores. The feed material distributes itself throughout the porouselectrode and migrates to near the outer surface to form a three-phaseboundary of feed, electrolyte, and electrode element, at which point thereaction takes place. The product and unreacted feed then migrate up tothe portion of the electrode element above the electrolyte level wherethey are collected, without ever having broken out into the bulk of theelectrolyte. (The feed is momentarily in contact with the bulk of theelectrolyte when it bubbles out at the sparger.)

The porous portion of the porous elements of the electrode assemblies ofthe invention can be fabricated from any suitable conducting porouselectrolyte resistant material which is compatible with the system,e.g., nickel, iron, various metal alloys, and carbon, which is notwetted by the electrolyte. Porous carbon, which is economical andreadily available in ordinary channels of commerce, is presentlypreferred for said porous element. In many instances it is advantageousto provide a metal element in contact with the porous carbon element.For instance a porous carbon anode can have a nickel screen wrappedaround it. Various grades of porous carbon can be used in the practiceof the invention. it is preferred to employ porous carbon which has beenmade from carbon produced by pyrolysis, and not graphitic carbon. Theelectrodes of the invention can be fabricated in any suitable shape ordesign, but must be arranged or provided with a suitable means forintroducing the feed reactant material into the pores of the porouselement thereof. This is ordinarily accomplished by positioning thesparger feed section, which is in communication with the feed supply,adjacent the bottom of the porous reaction section of the electrodeelement.

The electrode assemblies of the invention can be employed in anyconvenient cell configuration or electrode arrangement. The onlyrequirements are that the cell body and the electrodes in the cell befabricated of materials which are resistant to the action of thecontents of the cell under the reaction conditions. Materials such assteel, iron, nickel, polytetrafiuoroethylene (Teflon), carbon, and thelike, can frequently be employed for the cell body. When a nonporouscathode or a nonporous anode is employed which is not fabricated inaccordance with this invention (along with a porous anode or a porouscathode of the invention), said nonporous cathode or nonporous anode canbe fabricated in any suitable shape or design and can be made of anysuitable conducting material such as iron, steel, nickel, alloys of saidmetals, carbon, and the like. For example, said nonporous cathode can befabricated from a metal screen or gauze, a perforated plate, and canhave a shape complementary to the shape of the porous anode.

The electrode assemblies of the invention can be employed in a widevariety of electrochemical conversion processes in which the porouselectrode is not wetted by the particular electrolyte being used, andwherein the reaction takes place within the confines of the electrode.Some examples of such processes are electrochemical halogenation,electrochemical cyanation, and cathodic conversions such as thereduction of alcohols to hydrocarbons or the reduction of acids toalcohols. One electrochemical conversion process in which the electrodeassemblies of the invention are particularly valuable is theelectrochemical fluorination of fluorinatable materials in the presenceof an essentially anhydrous liquid hydrogen fluoride containingelectrolyte. Thus, for purposes of convenience, and not by way oflimitation, the electrode assemblies of the invention are primarilydescribed in terms of being employed as an anode in the electrochemicalfluorination of fluorinatable materials when using said hydrogenfluoride containing electrolyte.

As referred to hereinabove, the instant invention is applicable toelectrochemical conversion reactions wherein a current-conductingessentially anhydrous liquid hydrogen fluoride electrolyte iselectrolyzed in an electrolysis cell provided with a cathode and aporous anode (preferably porous carbon), a fluorinatable organiccompound is introduced into the pores of said anode and therein at leasta portion of said organic compound is at least partially fluorinatedwithin the pores of said anode, and fluorinated compound products arerecovered from said cell. The present invention provides im provedelectrode assemblies which are especially suited to be employed asanodes in said process to produce partially fluorinated materials and/orto fluorinate organic compounds with little or no scission of carbon tocarbon bonds.

Very few organic compounds are resistant to fluorination. Consequently,a wide variety of feed materials, both normally liquid and normallygaseous compounds, can be used as feedstocks in this process. Organiccompounds which are normally gaseous or which can be introduced ingaseous state into the pores of a porous anode under the conditionsemployed in the electrolysis cell, and which are capable of reactingwith fluorine, are presently preferred as starting materials. However,starting materials which are introduced into the pores of the anode inliquid state can also be used. Generally speaking, desirable organicstarting materials which can be used are those containing from one toeight, preferably one to six, carbon atoms per molecule. However,reactants which contain more than eight carbon atoms can also be used.If desired, suitable feed materials having boiling points above celloperating temperatures can be passed into the pores of the porous anodein gaseous state by utilizing a suitable carrier gas. Thus, a suitablecarrier gas can be saturated with the feed reactant (as by bubbling saidcarrier gas through the liquid reactant), and then passing the saturatedcarrier gas into the pores of the porous anode. Suitable carrier gasesinclude the inert gases such as helium, argon, krypton, neon, xenon,nitrogen, etc. Normally gaseous materials such as hydrocarbonscontaining from one to four carbon atoms can also be used as carriergases. These latter gases will react, but in many instances this willnot be objectionable. The above-described carrier gases, andparticularly said inert gases, can also be used as diluents for thefeedstocks which are normally gaseous at cell operating conditions.

Some general types of starting materials which can be used include,among others, the following: alkanes, alkenes, alkynes, amines, ethers,esters, mercaptans, nitriles, alcohols, aromatic compounds, andpartially halogenated compounds of both the aliphatic and aromaticseries. It will be understood that the above-named types of compoundscan be either straight chain, branched chain, or cyclic compounds.Partially chlorinated and the partially fluorinated compounds are thepreferred partially halogenated compounds. The presently preferredstarting materials are the saturated and unsaturated hydrocarbons(alkanes, alkenes, and alkynes) containing from one to six carbon atomsper molecule. The presently more preferred starting materials are thenormally gaseous organic compounds, and particularly said saturated andunsaturated hydrocarbons, containing from one to four carbon atoms permolecule.

Since fluorine is so reactive, no list of practical length could includeall starting materials which can be used. However, representativeexamples of the above-described starting materials include, amongothers, the following: methane; ethane; propane; butane; isobutane;pentane; n-hexane; n-octane; cyclopropane; cyclopentane; cyclohexane;cyclooctane; 1,2-dichloroethane; l-fluoro-2-chloro-3-methylheptane;ethylene; propylene; cyclobutene; cyclohexene; 2-methylpentene-l;2,3-dimethylhexene-2; butadiene; vinyl chloride; 3- fluoropropylene;acetylene; methylacetylene; vinylacetylene; 4,4-dimethylpentyne-2; allylchloride; methylamine;

ethylamine; diethylamine; 2-amino-3-ethylpentane; 3- bromopropylamine;triethylamine; dimethyl ether; diethyl ether; methylethyl ether;methylvinyl ether; 2-iodoethylmethyl ether; di-n-propyl ether; methylformate; methyl acetate; ethyl butyrate; ethyl formate; n-amyl acetate;methyl 2-chloroacetate; methyl mercaptan; ethyl mercaptan; npropylmercaptan; Z-mercaptohexane; 2-methyl-3-mercaptoheptane; acetonitrile;propionitrile; n-butyronitrile; acrylonitrile; n-hexanonitrile;methanol; ethanol; isopropanol; n-hexanol; 2,2-dimethylhexanol-3;n-butanol; ethylenebromohydrin; benzene; toluene; cumene; o-xylene;p-xylene, and monochlorobenzene.

In addition to such fluorinatable organic materials described above,carbon monoxide and oxygen can be used as feedstocks to provide carbonylfluoride and oxygen difluoride, respectively.

The electrochemical fluorination process is carried out in a medium ofhydrogen fluoride electrolyte. Although said hydrogen fluorideelectrolyte can contain small amounts of water, such as up to about 5weight per cent, it is preferred that said electrolyte be essentiallyanhydrous. The hydrogen fluoride electrolyte is consumed in the reactionand must be either continuously or intermittently placed in the cell.

Pure anhydrous liquid hydrogen fluoride is nonconductive. Theessentially anhydrous liquid hydrogen fluoride described above has a lowconductivity which, generally speaking, is lower than desired forpractical operation. To provide adequate conductivity in theelectrolyte, and to reduce the hydrogen fluoride vapor pressure at celloperating conditions, an inorganic additive can be incorporated in theelectrolyte. Examples of suitable additives are inorganic compoundswhich are soluble in liquid hydrogen fluoride and provide effectiveelectrolytic conductivity. The presently preferred additives are thealkali metal (sodium, potassium, lithium, rubidium, and cesium)fluorides and ammonium fluoride. Other additives which can be employedare sulfuric acid and phosphoric acid. Potassium fluoride, cesiumfluoride, and rubidium fluoride are the presently preferred additives.Potassium fluoride is the presently most preferred additive. Saidadditives can be utilized in any suitable molar ratio of additive tohydrogen fluoride within the range of from 114.5 to 1:1, preferably 1:4to 1:2. The presently most preferred electrolytes are those whichcorrespond approximately to the formulas KF'ZI-IF, KF-BHF, or KF-4HF.Such electrolytes can be conveniently prepared by adding the requiredquantity of hydrogen fluoride to KF-I-IF (potassium bifluoride). Ingeneral, said additives are not consumed in the process and can be usedindefinitely. Said additives are frequently referred to as conductivityadditives for convenience.

The electrochemical fluorination can be effectively and convenientlycarried out over a broad range of temperatures and pressures limitedonly by the freezing point and the vapor pressure of the electrolyte.Generally speaking, the fluorination process can be carried out attemperatures within the range of from minus 80 to 500 C. at which thevapor pressure of the electrolyte is not excessive, e.g., less than 250mm Hg. It is preferred to operate at temperatures such that the vaporpressure of the electrolyte is less than about 50 mm Hg. As will beunderstood by those skilled in the art, the vapor pressure of theelectrolyte at a given temperature will be dependent upon thecomposition of said electrolyte. It is well known that additives such aspotassium fluoride cause the vapor pressure of liquid hydrogen fluorideto be decreased an unusually great amount. A presently preferred rangeof temperature is from about 60 C. to about 105 C. Higher temperaturessometimes tend to promote fragmentation of the product molecules.

Pressures substantially above or below atmospheric can be employed ifdesired, depending upon the vapor pressure of the electrolyte asdiscussed above. In all instances, the cell pressure will be sufiicientto maintain the electrolyte in liquid phase. Generally speaking, theprocess is conveniently carried out at substantially atmosphericpressure. It should be pointed out that a valuable feature of theprocess is that the operating conditions of temperature and pressurewithin the limitations discussed above are not critical and areessentially independent of the type of feed employed in the process.

For purposes of efficiency and economy, the rate of direct current flowthrough the cell is maintained at a rate which will give the highestpractical current densities for the electrodes employed. Generallyspeaking, the current density will be high enough so that anodes ofmoderate size can be employed, yet low enough so that the anode is notcorroded or disintegrated under the given current flow. Currentdensities within the range of from 30 to 1000, or more, preferably 50 to500 milliamps per square centimeter of anode geometric surface area canbe used. Current densities less than 30 milliamps per square centimeterof anode geometric surface area are not practical because the rate offluorination is too slow. The voltage which is employed will varydepending upon the particular cell configuration employed and thecurrent density employed. In all cases, under normal operatingconditions, however, the cell voltage or potential will be less thanthat required to evolve or generate free or elemental fluorine. Voltagesin the range of from 4 to 12 volts are typical. The maximum voltage willnot exceed 20 volts per unit cell. Thus, as a guide, voltages in therange of 4 to 20 volts per unit cell can be used.

As used herein unless otherwise specified, the term anode geometricsurface" refers to the outer geometric surface area of the porous carbonelement of the anode which is exposed to electrolyte and does notinclude the pore surfaces of said porous element.

The feed rate of the fluorinatable material being introduced into thepores of the porous carbon element of the anode is an important processvariable in that, for a given current flow or current density, the feedrate controls the degree of conversion. Similarly, for a given feedrate, the amount of current flow or current density can be employed tocontrol the degree of conversion. Gaseous feed rates which can beemployed will preferably be in the range of from 0.5 to 10, millilitersper minute per square centimeter of anode geometric surface area. Withthe higher feed rates, higher current density and current rates areemployed. Since the anode can have a wide variety of geometrical shapes,which will affect the geometrical surface area, a sometimes more usefulway of expressing the feed rate is in terms of anode cross-sectionalarea (taken perpendicular to the direction of flow). On this basis, fora typical anode, the above range would be 25 to 500 milliliters perminute per square centimeter of cross-sectional area.

The actual feed rate employed will depend upon the type of carbon usedin fabricating the porous element of the anode as well as several otherfactors including the nature of the feedstock, the conversion desired,current density, etc., because all these factors are interrelated and achange in one will affect the others. The feed rate will be such thatessentially none of the feed, after having been absorbed, leaves theanode to form bubbles which escape into the main body of theelectrolyte. Essentially all of the feedstock and/or reaction producttravels within the carbon anode via the pores therein until it reaches acollection zone within the anode from which it is removed via a conduit,or until it exits from the anode at a point above the surface of theelectrolyte.

The more permeable carbons will permit higher flow rates than the lesspermeable carbons. Similarly, electrode shapes, electrode dimensions,and manner of disposition of the electrode in the electrolyte will alsohave a bearing on the flow rate. Thus, owing to the many different typesof carbon which can be employed and the almost infinite number ofcombinations of electrode shapes, dimensions, and methods of dispositionof the electrode in the electrolyte, there are no really fixed numericallimits on the flow rates which can be used. Broadly speaking, the upperlimit on the flow rate will be that at which breakout of feedstockand/or fluorinated product begins along the immersed portion of theelectrode element. Unless otherwise specified, breakout" is defined asthe formation of bubbles of feedstock and/or fluorinated product on theouter immersed surface of the electrode element with subsequentdetachment of said bubbles wherein they pass into the main body of theelectrolyte. Broadly speaking, the lower limit of the feed rate will bedetermined by the requirement to supply the minimum amount of feedstocksufficient to prevent evolution of free fluorine. As a practical guideto those skilled in the art, the gaseous flow rates can be within therange of from 3 to 600, preferably 12 to 240, cc (STP) per minute persquare centimeter of cross-sectional area (taken perpendicular to thedirection of flow).

Although the electrolyte is nonwetting, there will be some penetrationof the large pores of the electrode element by the hydrogen fluorideelectrolyte as previously noted. The amount of said penetration willdepend upon the pore size and other factors. The larger size pores aremore readily penetrated. It has been found that porous carbon anodes asdescribed herein can be successfully operated when up' to about 40 or 50per cent of the pores have been penetrated by liquid I-IF electrolyte.

The feed material and the products obtained therefrom are retained inthe cell for a period of time which is generally less than one minute.Because the residence time is comparatively short and is especiallyuniform, the production of the desired products is facilitated. Thefluorinated products and the unconverted feed are passed from the celland then are subjected to conventional separation techniques such asfractionation, solvent extraction, adsorption, and the like, forseparation of unconverted feed and reaction products. Unconverted orinsufficiently converted feed materials can be recycled to the cell forthe production of more highly fluorinated products, if desired.Perfluorinated products, or other products which have been too highlyfluorinated, can be burned to recover hydrogen fluoride which can bereturned to the cell, if desired. By-product hydrogen, produced at thecathode, can be burned to provide heat energy or can be utilized inhydrogen-consuming processes such as hydrogenation, etc.

Referring now to the drawings, particularly FIG. 1, there is shown inschematic representation a complete electrochemical conversion cellhaving a porous electrode element 12. In the bottom of porous anode 12is cavity 14. Feed from line 16 is introduced into sparger 18 which ispositioned within the bulk of the electrolyte within cavity 14. Sparger18 is held in place by electrically insulating connection strap 15.Current collector 20 is embedded in the upper portion of porouselectrode element 12. Said porous electrode element 12 is disposed incell container 22. The upper end of said porous electrode element isabove the level of the electrolyte in said container as depicted byreference character 24. Thus, the upper end surface of porous electrodeelement 12 comprises a second surface for withdrawing unreactedfeedstock and product from the pores of the porous electrode element 12,the inner wall of cavity 14 comprising a first surface for theintroduction of feed materials into the pores of said porous ele ment12. Conduit 26 comprises a second conduit means for withdrawing productand unreacted feedstock from within the pores of porous electrodeelement 12. If desired, the space above the electrolyte can be dividedby a partition 28 extending from the top of the cell to below the levelof the electrolyte to keep the anode products separated from the cathodeproducts; or a conventional cell divider can be employed to divide thecell into an anode compartment and a cathode compartment. However, sucha divider is not essential. A separate conduit 27 removes materialgenerated at cathode 29.

Referring now to FIG. 2, there is shown an enlarged view of the anode ofFIG. 1, partially in section, having a body portion 30 of relativelyhigh pore diameter porous carbon, elongated cavity 14 and sparger 18made of relatively low pore diameter porous carbon. Running along thecenter of sparger 18 is channel 36 which terminates just short of theend of the sparger.

In FIG. 3 there is shown a porous electrode-sparger arrangement similarto that of FIG. 2 except the sparger 37 has a configurationcomplementary to that of the cavity. While not specifically shown inthis figure, the end of the sparger is closed off in all embodiments bya portion similar to portion 35 of FIG. 2.

In FIG. 4 there is shown in section the lower portion of a porouselectrode in which the sparger is disposed in a large channel drillednear the bottom of the anode parallel to the bottom of the anode.Electrolyte fills the annular space 38. This figure is taken along aline near the far end of the channel so as to show a drain hole 39 whereannular area 38 is in open communication with the bulk of theelectrolyte.

In FIG. 5 there is shown a cylindrical porous electrode partially insection wherein a cavity is formed by drilling a hole 40 in the bottomof the anode. Disposed within this cavity is sparger 42, the feed beingcarried to this sparger via line 44.

Referring now to FIG. 6 there is shown a cross-sectional view of thelower portion of a rectangular slab-type porous electrode having aninner core section 46 of relatively low pore diameter carbon; affixed oneach side of this core section are slabs 48 of relatively high porediameter carbon. Slabs 48 extend down below the end of core 46 thusforming an elongated cavity 50. Feed is introduced into channel 52 ofsparger 54 by means of line 56 which comes in at an angle from the side.Sparger 54 is comprised of relatively low pore diameter carbon identicalto that portion making up core 46.

Referring now to FIG. 7, there is shown the lower portion of a porouscarbon electrode 58 having a sparger 60 disposed just beneath the flatbottom 62 of electrode 58.

Referring now to FIG. 8, there is shown a cylindrical electrode inaccordance with the instant invention having outer sections 64 ofrelatively high pore diameter carbon, a sparger 66 made of relativelylow pore diameter carbon and integrally affixed to the anode, and a coreportion 68 comprised of impervious carbon. Centrally disposed throughsaid core is hollow copper tube 70 which serves the dual function oftransmitting the feed material into channel 72 of sparger 66 and also ofserving as the current collector.

Referring to FIG. 9, there is shown a rectangular electrode inaccordance with the instant invention in which sparger elements 74 arescrewed into an extension of core section 76. This section is takenlongitudinally; as can be seen high pore diameter sections 77 and 79 donot extend below core 76 at the ends. If desired, sections 77 and 79 canbe made to extend below core 76. While not shown in this figure, highpore diameter slabs are laminated to the sides of core 76 and extendbelow core 76 along these sides as shown in the electrode shown in FIG.6.

In FIG. 10 there is shown another cylindrical electrode embodiment ofthe instant invention wherein sparger element 78 is removably attacheddirectly to copper tube 80 by means of a screw connection 82.

Many conventional parts such as electrical circuitry, flow regulators,and the like have not been shown for the purpose of simplicity, buttheir inclusion is understood by those skilled in the art and is withinthe scope of the invention. Similarly, the schematic representationsshow relative dimensions which may or may not be optimum for specificsituations. For example, the distance between anode and cathode can bemuch smaller than what is illustrated.

EXAMPLE I A slab of porous carbon (National Carbon NC-60 having aporosity of about 50 per cent, a permeability of about 6 darcys, and anaverage pore size of about 45 microns), measuring 6 X 14 X 1% inches,was fitted with two copper current collectors inserted 5 inches into thetop of the carbon. The bottom of the slab was slotted with about a l X 1inch channel. A sparger of a tight porous carbon (Stackpole 139 having aporosity of about 30 per cent, a permeability of about 0.056 darcys, andpores of 01-10 microns averaging about 3 microns), measuring about 6 X lX inches was suspended. with Teflon straps, directly beneath the carbonelectrode and within the channel but not in electrical contact. In thesparger was a feed distribution channel, a lateral one-fourth inch holeextending almost the length of the sparger. This hole was connected witha fitting to a one-fourth inch Teflon-jacketed copper feed tube. Theelectrode configuration, thus, was similar to that of FIG. 3 except thechannel and sparger were rectangular rather than triangular.

The above-described electrode was used as an anode in an electrochemicalfluorination cell. It was presoaked in ethylene dichloride (EDC) andimmersed about 12 inches in KF *2l-1F electrolyte maintained at about 93C. The cathode was an iron grid. Ethylene dichloride was fed into theanode by means of the sparger. The ethylene dichloride bubbles leavingthe sparger were rapidly absorbed by the bottom of the porous carbonanode. As the feed material passed upward through the anode, it wasfluorinated and it finally left the anode through that portion of theanode above the surface of the electrolyte. Hydrogen was evolved at thecathode and the total cell effluent was conducted to a recovery system.HF was replenished in the electrolyte as it was consumed.

After being on stream for about 24 hours, a sample of the cell effluent,after the hydrogen was removed, was taken during a hour period andsubjected to gas-liquid chromatography for analysis. The cell conditionsduring this sampling period were as follows:

EDC Feed Rate 4.86 moles/hr.

Current 250 amp Voltage 8l0 volts Faradays/mole 1.91 EDC Conversion33.65% EDC Efficiency (to Freon l 14 and its precursors) 85.12% HFEfficiency 85.18%

The products obtained rrom the cell were found to be as follows:

The data above show that the electrode system of the present inventionis capable of efficiently fiuorinating an organic feedstock at very highconversions but with very little losses due to scission of carbon tocarbon bonds.

EXAMPLE II The above electrochemical fluorination of ethylene dichloridewas repeated using the same anode and sparger configuration but atalmost twice the current density and feed rate. The essential data fromthis run are as follows:

EDC Rate 8.81 moles/hr. Voltage 8-10 volts Current 400 amp Faradays/mole1.69

EDC Efi'iciency 87.82%

HF Efiiciency 88.33%

EDC Conversion 32.6%

The above test illustrates operation of the invention at a very highcurrent density.

EXAMPLE Ill In another test in which ethylene dichloride was fluorinatedto Freon 114 and related products, the anode was similar to that ofExample 1 except that a groove having a triangular cross section was cutinto its bottom. The porous carbon sparger, of Stackpole 139 material,was ofa corresponding triangular cross section, about 1% inches on anedge, which was neatly fitted and cemented into the cavity of theelectrode using a conventional carbon cement (National Carbon C-3cement) which was both conducting and porous. As in Example 1, thistriangular sparger contained a drilled one-fourth inch lateral holewhich was in communication with the feed supply. Thus, this electroderesembled that of FIG. 3.

Under conditions largely similar to that of preceding examples, theethylene dichloride was satisfactorily converted over a 24-hour periodat 8-10 volts, 215 amp, and about a 4.8 mole/hour feed rate.

This run illustrates that the sparger of the anode assembly can also beoperated when in close electrical contact with the anode.

EXAMPLE IV A porous carbon electrode having a sandwich constructionusing two types of porous carbon was tested. A slab of the previouslydescribed Stackpole 139 porous carbon measuring 6 X 12 X 3 4 inches wasbonded between two pieces of porous carbon (National Carbon NC-45 havingan average pore size of about 55 microns, a permeability of about 20darcys, and an average porosity of about 50 per cent) which measured 6 X14 X inches using National Carbon C3 cement. This laminate was driedovernight at 2l5-220 F. The bottom two inches of the 14 inch long NC-45sections extended below the 12 inch long inner core and formed a channelfor the feed sparger. The sparger was a piece of Stackpole 139 carbonmeasuring 1 X 6 X inches and containing a five-sixteenth-inch holethrough most of its length for the introduction of the feed. The loweredge of this feed sparger was even with the lower edge of the NC-45skirt, being held in position by Teflon and plates fastened to both thesparger and the electrode. A void measuring 6 X 1 X 4 inches thusremained between the sparger and the electrode. The sparger was notelectrically connected. Two copper current conductors were convenientlymounted within the core, extending about 5 inches into the Stackpole 139section. The electrode, thus, resembled that of FIG. 6.

The above-described electrode was used as an anode in theelectrochemical fluorination of ethylene dichloride, being im mersedabout 12 inches into the KF'ZHF electrolyte in the same cell describedin Example I. The cell operated satisfactorily for about 5 days at 8-9volts and at a current density of 200 ma/cm producing substantialamounts of Freon 114 and related products.

EXAMPLE V A 14 X 1% inch OD cylinder of porous carbon (National CarbonPC 45) having a flat bottom and fitted with a copper current collectorwas employed as an anode in an electrochemical conversion operationsimilar to that of Example 1. The sparger was a short cylinder ofthree-fourths inch OD porous carbon (Stackpole 139) and was disposeddirectly under the flat bottom of the porous carbon anode in a mannersimilar to that shown in H6. 7 except that the anode was cylindricalrather than rectangular. The anode immersion was 10 inches and thesparger was spaced about one-eighth inch from the anode. Ethylenedichloride was introduced into the interior of the sparger undersufficient pressure to cause it to bubble out into the electrolyte whereit immediately rose to contact and to be absorbed by the porous anodewherein it was fluorinated, at a current density of 400 ma/cm toproducts similar to those obtained in Example 1.

EXAMPLE VI A porous carbon anode was constructed from a cylinder ofporous carbon (NC-45) measuring 14 inches long and 1% inches indiameter. A copper pin was inserted into the top of the cylinder as acurrent collector and a three-fourths inch diameter hole was drilledaxially into the bottom of the cylinder to provide a cavity aboutthree-fourths inch deep.

The above-described electrode was used as an anode in an electrochemicalfluorination cell which contained KF'ZHF as the electrolyte maintainedat 94-l C., an iron cathode, and an ethylene dichloride feed tube whichterminated in a porous polytetrafluoroethylene sparger in the form of adisc about three-eighths inch in diameter and three-sixteenths inch inthickness. The sparger was located directly beneath the cavity in amanner similar to that of FIG. 5. The anode was submerged 4 inches inthe electrolyte and, during operation, the fluorinated products andunconverted feed material exited the anode through the portion of theporous carbon which extended above the surface of the electrolyte.Hydrogen was evolved at the cathode.

Ethylene dichloride was successfully fluorinated with this electrode andcell arrangement in a run of about hours duration, at a current level of42-49 amps, at about 7.8 volts, and at a feed rate of about 100 mlethylene dichloride per hour.

While this invention has been described in detail for the purpose ofillustration, it is not to be construed as limited thereby but isintended to cover all changes and modifications within the spirit andscope thereof.

We claim:

1. A process for the electrochemical conversion of a feedstock, whichprocess comprises: passing an electric current through acurrent-conducting electrolyte composition contained in anelectrochemical cell provided with a first electrode element and aporous second electrode element which porous electrode element is notwetted by said electrolyte; releasing said feedstock into saidelectrolyte from a plurality of points, and in the form of a multitudeof very small bubbles, at a point within the bulk of said electrolyteand adjacent a bottom end portion of said porous electrode element;thereafter absorbing said feedstock into the pores of said porouselectrode element at said bottom end portion; distributing saidfeedstock through said porous electrode element and therein at leastpartially reacting at least a portion of said feedstock; and recoveringproduct and any remaining un' reacted feedstock from within said poresof said porous electrode element at a point spaced away from said bottomend portion thereof.

2. A process according to claim 1 wherein said first electrode elementis an anode and said porous second electrode element is a cathode.

3. A process according to claim 2 wherein said porous cathode comprisescarbon and said feedstock is released from a porous sparger.

4. A process according to claim 3 wherein said sparger also comprisescarbon and is disposed within an open cavity formed in said bottomportion of said cathode.

5. A process for the electrochemical conversion of an organic compoundfeedstock, which comprises: passing an electric current through acurrent-conducting electrolyte composition contained in anelectrochemical cell provided with a cathode and a porous anode whichporous anode is not wetted by said electrolyte; releasing said feedstockinto said electrolyte from a plurality of points, and in the form of amultitude of very small bubbles, at a point within the bulk of saidelectrolyte and adjacent a bottom end portion of said anode; thereafterabsorbing said feedstock into the pores of said porous anode at saidbottom end portion; distributing said feedstock through said porousanode and therein at least partially reacting at least a portion of saidfeedstock; and recovering product and any remaining unreacted feedstockfrom within said pores of said anode at a point spaced away from saidbottom end portion thereof. I

6. A process according to claim 5 wherein said electrolyte compositioncomprises essentially anhydrous liquid hydrogen fluoride, and whereinsaid product is at least partiaily fluorinated.

7. A process according to claim 6 wherein said porous anode comprisescarbon and said feedstock is released from a porous sparger.

8. A process according to claim 7 wherein said sparger also comprisescarbon and is disposed within an open cavity formed in said bottomportion of said anode.

9. A process according to claim 3 wherein said sparger comprises porouscarbon and is electrically connected to said second electrode element.

10. A process according to claim 7 wherein said sparger comprises porouscarbon and is electrically connected to said anode.

2. A process according to claim 1 wherein said first electrode elementis an anode and said porous second electrode element is a cathode.
 3. Aprocess according to claim 2 wherein said porous cathode comprisescarbon and said feedstock is released from a porous sparger.
 4. Aprocess according to claim 3 wherein said sparger also comprises carbonand is disposed within an open cavity formed in said bottom portion ofsaid cathode.
 5. A process for the electrochemical conversion of anorganic compound feedstock, which comprises: passing an electric currentthrough a current-conducting electrolyte composition contained in anelectrochemical cell provided with a cathode and a porous anode whichporous anode is not wetted by said electrolyte; releasing said feedstockinto said electrolyte from a plurality of points, and in the form of amultitude of very small bubbles, at a point within the bulk of saidelectrolyte and adjacent a bottom end portion of said anode; thereafterabsorbing said feedstock into the pores of said porous anode at saidbottom end portion; distributing said feedstock through said porousanode and therein at least partially reacting at least a portion of saidfeedstock; and recovering product and any remaining unreacted feedstockfrom within said pores of said anode at a point spaced away from saidbottom end portion thereof.
 6. A process according to claim 5 whereinsaid electrolyte composition comprises essentially anhydrous liquidhydrogen fluoride, and wherein said product is at least partiallyfluorinated.
 7. A process according to claim 6 wherein said porous anodecomprises carbon and said feedstock is released from a porous sparger.8. A process according to claim 7 wherein said sparger also comprisescarbon and is disposed within an open cavity formed in said bottomportion of said anode.
 9. A process according to claim 3 wherein saidsparger comprises porous carbon and is electrically connected to saidsecond electrode element.
 10. A process according to claim 7 whereinsaid sparger comprises porous carbon and is electrically connected tosaid anode.